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Antiproton production in heavy ion collisions reflects subtle interplay between initial production and absorption by nucleons. Because the AGS energies (10--20 A·GeV/c) are close to the antiproton production threshold, antiproton may be sensitive to cooperative processes such as QGP and hadronic multi-step processes. On the other hand, antiproton has been proposed as a probe of baryon density due to large N{anti N} annihilation cross sections. Cascade models predict the maximum baryon density reaches about 10 times the normal nucleus density in central Au+Au collisions, where the strong antiproton absorption is expected. In this paper, the authors show systematic studies of antiproton production from p+A to Au+Au collisions.
We present antiproton production in 11.7 AGeV/c Au+Au collisions measured in a wide transverse-mass coverage from the AGS-E866 experiment. We show indications for strong absorption effects of antiprotons in Au+Au collisions through comparison with p+A and Si+A collisions, and centrality dependence in Au+Au collisions.
One of the main goals of high energy heavy ion physics is to establish the existence of a deconfined phase of nuclear matter--the quark-gluon plasma--at high temperatures or densities. One possible signature of such a phase transition, especially if it were first order, would be a larger source size or lifetime than a similar hadronic system. At current AGS energies, we attempt to form a quark- gluon plasma by achieving a high baryon density for a period of time in the center of the collision region. For a given density threshold, the size of this high density region should be a strong function of the impact parameter: the more central the event, the larger the high density region. Therefore, one possible signature of a quark-gluon plasma would be a sudden change in system lifetime or size as a function of the centrality of the collision. In this talk we present an intriguing effect which was not predicted for simple hadronic systems: a rapid increase of the HBT-measured source radius parameter for pion pairs with increasing centrality for Au-Au collisions at a beam momentum of 11.45 A GeV/c on a fixed target. Experience has shown, however, that we must be cautious in our interpretation. A complete understanding of the collision dynamics at a given energy must be built up from several measurements and new, but conventional, hadronic explanations must be considered for such unexpected effects. More study is needed, therefore, before any strong conclusions can be reached.
We present results on antiproton production obtained in the AGS experiments E858 and preliminary results of E878. The yields of antiprotons in Si + A collisions are shown to sale with number of first collisions. The rapidity distributions for all targets (Au, Cu and Al) and both beams (si at 14.6 GeV/c and A at 11. GeV/c) have gaussian shapes peaking at y{sub NN} and with similar standard deviations. From E878 we report a difference in the shape of the antiproton rapidity distributions obtained from two samples of the data populated with central and peripheral events respectively. In A induced reactions the A dependence of the antiproton yields is small.
BNL E910 has measured strange baryon production as a function of collision centrality for 17.5 GeV/c p-Au collisions. Collision centrality is defined by v1 the mean number projectile-nucleon interactions estimated from the ''grey'' track multiplicity. The measured [Lambda] yield increases faster than the participant scaling expectation for v ≤ 3 and then saturates. A simple parameterization of this dependence applied to nucleus-nucleus collisions reproduces the measured E866 km. and WA97 [Lambda] centrality dependent yields. The increase in [Lambda] production to v ≤ 3 is also evident for [Lambda]s which are leading baryons, in disagreement with predictions from RQMD.
Proceedings of the NATO Advanced Study Institute on [title], held in Bodrum, Turkey, Sept.-Oct. 1993. Leading researchers present new material and new results with regard to hot and dense nuclear matter. Essentially, they investigate how matter may have been formed and what its properties were just
We report on the rapidity and centrality dependence of proton and anti-proton transverse mass distributions from 197Au + 197Au collisions at √s{sub NN} = 130 GeV as measured by the STAR experiment at RHIC. Our results are from the rapidity and transverse momentum range of.